The region of the Eye constitutes its own reality, existing within both the material universe and the Warp. Although planets and star systems exist within the Eye, the laws of reality no longer apply. Time is a meaningless concept, and matter, thought, and energy are indistinct.

The worlds within the Eye are known as Daemon Worlds, and each constitutes its own bizarre sub-reality. At the very center of the Eye lies the “byssos”, a hole in the fabric of reality through which raw Chaos energy pours out.

The Warp and real space are indistinct and intermixed within the Eye, and the whole region is a maelstrom of psychic energy, impossible to navigate through. Imperial ships avoid the area around the Eye for thousands of light-years. Ships traveling too close to the Eye can be thrown far off-course – they can also be caught in temporal whirlpools which carry them backwards or forwards in time, or which trap them in limbo forever.

The Warp storms that disturb the Eye are so intense that there is little point in even trying to steer a ship in a particular direction. The Chaos renegades simply launch their ships into the swirling energies of the Warp, trusting fortune to carry them to their enemies. This makes Chaos attacks so random, sudden and unpredictable, often occurring on worlds far from the Eye.

The Eye offers a sanctuary to the worst forms of traitors and heretics forced to flee from Imperial justice.

For the Traitor Legions, the Eye of Terror has been their exile, sanctuary, and safe haven for ten thousand years, from which they strike out at opportune, seemingly random moments. The Eye is also sanctuary for the most heretical renegades, fugitives of Imperial justice, and traitors throughout the galaxy, and all are welcomed as fellow enemies of the Emperor and the Imperium.

Mortals within the Eye are constantly exposed to the effects of Chaos, physically warped so their bodies come to reflect their flawed natures; the Death Guard, for example, worship Nurgle, Chaos God of Decay, so that their bodies become bloated and putrid.

The Eye of Terror is not a natural phenomenon. The Eye was created by the psychic shock wave that accompanied the birth of the fourth Chaos God, Slaanesh, during the Fall of the Eldar.

The shock of the birth was so great it could not wholly be contained within the Warp, but spilled out into reality through the minds of the Eldar. Consequently, the Eye covers most of the region of the former Eldar Empire. Other zones of overlap were created, but the Eye is the most significant.

Sometime at the dawn of the Imperium but before the Horus Heresy, the Eye of Terror was discovered by Imperial explorers in what was presumably a fairly remote region of the galaxy, and Imperial scholars named is Cygnus X-1. The Eye didn’t come into prominence until it was later discovered by the Word Bearers, who had arrived officially for conquest, but actually on a personal mission for renewed faith, and it was here that they discovered the “Primordial Truth”. It would later be visited by the Emperor’s Children and the Iron Warriors, intent on an expedition within the eye for the search of the Angel Exterminatus. Before embarking upon this journey, Perturabo had formally named the Eye of Terror.

The Imperial world of Cadia lies nearest to the best-known stable gateway into the Eye; consequently, it is the most fortified and militarized world in the Imperium, the first line of defense against Chaos incursions into real space. It would seem that ships exit through this gateway far more often than they enter it.

Abaddon the Despoiler led an attack through the Eye of Terror during a massive narrative campaign that decided the fate of Cadia and many other systems.